A bandgap circuit or simply, “bandgap” is an electronic circuit that generates an output voltage that is approximately temperature-invariant. The reference voltage signal may also be termed a precision voltage signal. A bandgap circuit may be part of a larger integrated circuit (IC). In an IC, a bandgap circuit may provide reference voltages for other voltage-sensitive circuits within the chip. A bandgap circuit may be tuned or “trimmed” to generate a precision reference voltage signal for a predetermined operating temperature. Conventional trimming operations occur during IC manufacture and validation processes. Although bandgap circuits may be trimmed to provide a precise reference voltage, traditional trimming techniques are time-consuming, costly, and may only provide a limited temperature range wherein the bandgap's output voltage remains constant.
A trimming technique known as a “temperature trim” may involve heating a chip from a first temperature to a second temperature and adjusting the bandgap's output voltage at each temperature to provide the desired reference voltage. For a limited range of temperature values around the first and second temperature, the bandgap's output will be accurate. However, as the temperature diverges from the first and/or second temperature, the bandgap reference voltage may diverge in a non-linear manner away from the desired reference voltage. In turn, the voltage-sensitive circuits receiving the bandgap reference voltage may malfunction throughout such divergent temperature ranges.
Beyond bandgap reference voltage nonlinearity issues, temperature trimming requires physically heating each of a chip to perform the trim. Such trimming operations require ICs to be loaded into a machine and tested. Once the chip is heated to the desired temperature, then the reference voltage may be trimmed by performing a number of trimming operations. Thus, a temperature trim may require several seconds of time to heat and trim a chip to a desired bandgap reference voltage. Since trimming operations are prolonged, temperature trimming limits the number of ICs that can be manufactured per unit time. As the number of chips that must be trimmed increases, the time required to perform a temperature trim on the lot of chips may scale in kind.
Accordingly, there is a need in the art for trimming a bandgap circuit that provides an increased temperature-invariance range for a bandgap reference voltage within a minimized trimming time.